1. Field of the Invention
This invention relates to a catadioptric lens barrel which can be attached to an optical projection unit, such as a projection exposure apparatus used to manufacture semiconductor wafers. More particularly, the present invention relates to a catadioptric lens barrel structure including its support structure, the lens barrel structure comprising a plurality of lens barrels aligned in parallel, and at least one transverse lens barrel connecting the plurality of lens barrels.
2. Description of the Related Art
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end of the lens barrel to the other. The lens barrel may include a sturdy threaded body and durable metal retaining rings, often referred to as xe2x80x9csub-barrels,xe2x80x9d to carry a series of lens holders, commonly referred to as xe2x80x9ccells.xe2x80x9d One type of lens barrel is known as a catadioptric lens barrel. A catadioptric lens barrel contains not only refractive elements, such as lenses, but also reflective elements, such as mirrors.
Both of these lens barrel designs are used in conventional optical systems. For example, optical projection units often have a lens barrel and may be used in a projection exposure apparatus for production of semiconductor wafers. The projection exposure apparatus includes a reticle positioned near an entrance end of the lens barrel and a semiconductor wafer positioned near an exit end. The projection exposure apparatus shines light through the reticle, photographically reduces a pattern on the reticle, and sequentially transfers the pattern, through the lens barrel, onto a predetermined area on the semiconductor wafer. The semiconductor wafer is a silicon wafer with a photo-sensitive coating or layer for making semiconductor devices, such as microprocessor or memory chips.
A catadioptric lens barrel system using two or more lens barrels, arranged in parallel, offers benefits not found in conventional single barrel systems. The parallelism of the lens barrels reduces the overall height of the lens barrel, but increases the overall width. Reduced height is important for many reasons, such as for ease of transport. This type of catadioptric lens barrel design, however, poses several problems. First, keeping proper alignment of a plurality of lens barrels can be difficult. Second, the focus depth of the projection system changes as temperature changes. Coefficients of thermal expansion of the lens barrels, including their internal components, and the indices of refraction of all lens materials vary with temperature. Errors related to these factors collectively alter the focusing properties of the optical system. Third, the lens barrel structure tends to be more sensitive to movement or vibration than conventional single barrel designs.
In light of the foregoing, there is a need for a catadioptric lens barrel structure that holds the lens barrels stabily and accurately, and minimizes distortion errors due to temperature changes, vibrational, or other external forces, so that the resulting image remains focused as it is transferred and reduced from the reticle to the wafer.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, one aspect of the invention is directed to a lens barrel structure for use in a projection exposure apparatus in semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The lens barrel structure comprises a plurality of lens barrels and a support structure. Each lens barrel has a length, an optical axis, and a center plane. The center plane runs perpendicular to the corresponding optical axis at a position half-way along the length of the corresponding lens barrels. The support structure supports each lens barrel substantially near the center plane of the corresponding lens barrel, which provides enhanced stability.
A second aspect of the invention is directed to a method for making a lens barrel structure, which in one embodiment is used in projection exposure apparatus in a semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The method comprises the step of disposing a plurality of lens barrels, each lens barrel having a length, an optical axis, and a center plane. The optical axis runs along the length of the lens barrel. The center plane runs perpendicular to the corresponding optical axis at a position half way along the length of the corresponding lens barrel. The method also comprises the step of providing a support structure for securing the plurality of lens barrels. The support structure secures each lens barrel substantially near the center plane of the corresponding lens barrel, which provides enhanced stability.
A third aspect of the invention is directed to a lithography system for use in a semiconductor manufacturing. The lithography system reduces a pattern on a reticle through a projection exposure apparatus to a semiconductor wafer. The lithography system comprises a lens barrel structure. The lens barrel structure comprises a plurality of lens barrels and a support structure. Each lens barrel has a length, an optical axis, and a center plane. The center plane runs perpendicular to the corresponding optical axis at a position half-way along the length of the corresponding lens barrels. The support structure supports each lens barrel substantially near the center plane of the corresponding lens barrel, which provides enhanced stability.
A fourth aspect of the invention is directed to a lens barrel structure made of particular materials, and maybe used in a projection exposure apparatus in semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The lens barrel structure comprises a plurality of lens barrels and a support structure for supporting the plurality of lens barrels. The support structure is made of a material having a low coefficient of thermal expansion, such as 6 ppmt/xc2x0 C. or below. The low coefficient of thermal expansion of the material reduces the effects of environmental changes on the lens barrel structure.
A fifth aspect of the invention is directed to a method for making a lens barrel structure made of particular materials, which may be used in a projection exposure apparatus in semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The method comprises the steps of disposing a plurality of lens barrels, and providing a support structure for securing the plurality of lens barrels. The support structure is made of a material having a low coefficient of thermal expansion, such as 6 ppm/xc2x0 C. or below. The low coefficient of thermal expansion of the material reduces the effects of environmental changes on the lens barrel structure.
A sixth aspect of the invention is directed to a lithography system for use in semiconductor manufacturing, the lithography system reducing a pattern on a reticle through a projection exposure apparatus to a semiconductor wafer. The lithography system comprises a lens barrel structure. The lens barrel structure comprises a plurality of lens barrels and a support structure for supporting the plurality of lens barrels. The support structure is made of a material having a low coefficient of thermal expansion, such as 6 ppm/xc2x0 C. or below. The low coefficient of thermal expansion of the material reduces the effects of environmental changes on the lens barrel structure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims.